Filters are used in many applications to remove impurities from a fluid. In the case of water treatment, filters are often employed to selectively remove minerals, chemicals, and other materials. Some of these filters, such as carbon filters which are used to improve the taste and odor of water, gradually become exhausted during use. In particular, the activated carbon housed within the filter eventually becomes saturated and can no longer remove the intended impurities. If the filter is not replaced, the water quality degrades. With many, if not most, of these filters, the user does not recognize the need for replacement until the water quality suffers substantially.